so what is your favorite instance and why? mine is ulduar because of its nice tuning with hard and normal modes, ofcourse this no longer applies because of the massive overgearing but it was good during 3.1, when you only had 200 gear from heroics. there were also optional bosses and it was easy enough for normal modes and hard enough for hard modes (yogg+0 / algalon anyone?).
the artwork design, models and architecture were also stunning although after a while the trash felt a bit too much.